1. Field of the Invention
This invention relates to fatty-acid-free syndet soaps containing alkyl and/or alkenyl oligoglycosides and starch.
2. Description of the Related Art
Bar soaps play an important part in personal hygiene. Today, bar soaps are industrially produced by continuous saponification of free fatty acids with alkalis, concentration of the basic soaps and spray drying. A distinction is drawn between true alkali soaps, which contain only fatty acid salts and optionally free fatty acids, and so-called "combination bars", i.e. bar soaps which--in addition to fatty acid salts--contain other synthetic surfactants, generally fatty alcohol ether sulfates or fatty acid isethionates. By contrast, a special position is occupied by so-called "syndet bars" which, apart from impurities, are free from fatty acid salts and contain only synthetic surfactants.
In Germany alone, several million bars of soap for personal hygiene are sold annually. However, the commercial requirements which these mass consumption articles are expected to satisfy are becoming increasingly more stringent. Bar soaps are required not only to clean, but also to care for the skin, i.e. to prevent the skin from drying out, to "ref at" the skin and to protect it against outside influences. The soap is of course expected to be particularly compatible with the skin, but at the same time to produce an abundant and creamy foam in use and to have a pleasant feeling on the skin. In this connection, manufacturers of bar soaps are constantly looking for new ingredients which satisfy these increased requirements.
In recent years, alkyl glucosides have acquired significance as new nonionic surfactants because they behave like anionic surfactants in many respects, for example in their foaming power, and at the same time show extremely high ecological and dermatological compatibility. Accordingly, it was logical to experiment with such surfactants in connection with bar soaps. For example, toilet soaps containing 1 to 20% by weight of alkyl polyglucosides and preferably 55 to 66% by weight of soap as builder are known from European patent application EP-A 0 463 912 (Colgate). Toilet soaps containing mild surfactants, including for example those of the alkyl polyglucoside type, are known from EP-A2 0 227 321, EP-B1 0 308 189 and EP-B1 0 308 190 (Procter & Gamble). Finally DE-A1 43 31 297 and DE-A1 43 37 031 (Henkel) describe fatty-acid-containing combination bars in which small quantities of alkyl polyglucosides are present. However, the bar soaps obtainable in accordance with the teaching of the prior art do not always develop enough foam and, in addition, are unsatisfactory in regard to foam consistency and, in particular, the feeling they have on the skin. In addition, if free fatty acids are used as refatting agents, extremely serious corrosion problems can occur in manufacturing equipment.
Accordingly, the problem addressed by the present invention was to provide bar soaps which would be free from the disadvantages described above. A particular factor to be taken into consideration in this regard was that the new bar soap compositions would also have to lend themselves to production on an industrial scale, i.e. they would be expected, for example, to show adequate, but not excessive moldability and would not have any tendency to form cracks on drying.